THE IDENTIFICATION OF LARVAE OF SOME SPECIES OF BARK BEETLES BREEDING IN CONIFEROUS TREES IN EASTERN CANADA A THESIS Submitted to the Faculty of Graduate Studies and Research of McGill University By J.B.Thomas In Partial Fulfilment of the Requirements for the Degree of Doctor of Philosophy October, 1954 TABLE OF CON'I»JTS I. Introduction . 1 II. Review of Literature ...................................... 3 III. Materials and Methods ..................................... 6 IV. Species of Bark Beetles Examined •••••••••••.•••••••••.•••• 9 V. Description of the External Anatomy of gylurgops pinifex (Fitch) as Typical of Scolytid Structure •••••••••••••••••• 12 A. General ............................................. 12 B. Head ................................................ 13 C. Mouthparts .......................................... 17 1. Labrum and Epipharyngeal Lining ................ 17 2. Mandible ....................................... le 3. Maxilla ........................................ 19 4. I...a.bium •••.•••.•••.•••••••••••••••••.•••••.••••• 20 Hypopharynx ••••• ............................... 21 D. Thorax and Abdomen .••..•.•.•.•........•...••.••..... 21 Dorsum ......................................... 22 Pleuron ........................................ 31 3. SterntlID •••.••••••••.••••••••••••.•••••••••••••• 33 VI. Comparative Anatomy of Species Studied . 36 A. General Discussion of Setal Nomenclature . 36 B. Integument Including Setal Pattern . 46 C. Head Capsule Including Setal Pattern ................ 53 D. Labrum ••••••••••.••••••••••••••••••••••••••••••••••• 61 E. Epipharyngeal Lining •••••••••••••••••••••••••.••.••• 62 F. Mandible ............................................ 64 G. Maxilla 65 H. Labf.um •••••••••••••••••••••••••••••••••••••••••••••• 66 VII. Identification of Genera and Some Species Examined ....... 70 Genus Conophthorus ...................................... 78 II Crypturgu.s •••......•.•.•••••........•••...•....•. 81 II Dendroctonus · . 84 II Dryocoetes •..........................•........... 89 II Gnathotrichus .................................... 92 II ByItt.rgops ••••..••••••..••••....•.•••.••..•••.•..• 95 II Orthotomicu6 · . 98 II Phloeosinus ...................................... 101 II Pityogenes ....................................... 103 II Pityokteines · . 106 II Polygraphus ...................................... 109 °11 Pityophthoru5 .................................... 111 II Scolytus ......................................... 114 " TryPodendron .••.......•.........................• 117 VIII. Observed and Recorded Hosts .............................. 120 IX. Average Length of Larvae and Adults of Species Examined••• 123 x• SlJIIlIIla17 •••••••••••••••••••••••••••••••••••••••••••••••••• 125 XI. Bibliography ............................................. 127 Plates I to XIV I. INTRODUCTION The use of the external anatomy of the larvae of bark beetles for the purpose of generic and specific identification has been neglected in the past. One reason for lack of interest in this particular phase of the study of bark beetles may lie in the biology of this group of insects where, in many cases, adults are present together with the larvae throughout most of the developmental period. However, there are occasions where larvae of more than one species feed in the same area of bark, and even though adults of all species represented are present, the percentage of each species cannot be estimated. This becomes important in population studies where, in order to obtain reasonably accurate results, all stages of each species must be counted. Also, there are occasions when the adults have emerged leaving only immature stages and here a key to the larvae is required. The small size of most bark beetle larvae of course necessitates the use of minute anatomical characters in separating one genus from another or species within a genus. This factor may lessen the usefulness of the keys for quantitative work since rapid examination of key characters is important. The use of minute and often obscure points of comparison should have no serious effect on the value of the key for qualitative purposes where the only need is to be able to say certain genera and species are repre­ sented in a particular community. An additional complication in the identity of bark beetle larvae occurs when weevil larvae, feeding in the same host, mingle with the bark beetle larvae. To date, there does not appear to be any positive means, other than rearing, of separating larvae of the families Scolytidae and Curculionidae. Identification of species of bark beetles has been made on the basis of imaginal characters, for which there are many out­ standing publications. There is also available in the literature, information on host specificity of many species as well as descriptions of the galleries and larval mines characteristic of certain genera. There has been to my knowledge no comprehensive study of the larvae of species of bark beetles occurring in eastern Canada for the purpose of separating them by anatomical characters. In the hope of establishing a satisfactory method of doing this and thereby adding a new working tool to those already available for identification of genera and species of Scolytidae, the results of my examination of the larvae of a number of spec~es of bark beetles are presented. While the number of species examined has not been as extensive as originally planned, it is my contention that the results of this study will begin to fill a gap in the published literature on bark beetles. The geographic boundaries of the areas, fraa which species being studied were selected, are not as restrictive as would appear at first since few species of bark beetles common to eastern fauna are found in the fauna of 'Western Canada, particularly in western Alberta and British Columbia. The restriction of this study to species breeding in coniferous trees is a natural one since I know of no one species which breeds in both coniferous and hardwood trees. When specimens or a sufficient number of species breeding in hardwood trees become available, it is hoped to make a separate study of the larval characteristics. - :3 - It is a pleasure to acknowledge the assistance of a number of collectors and institutions in providing material which I was unable to collect myself. Mr.N.R.Brown, University of New Brunswick, obtained a number of specimens of Dendroctonus simplex Lee. for me from the Science Service Laboratory, Fredericton, N.B. A further collection of this species was provided by Mr.A. T.Drooz of the Forest Insect Laboratory, Milwaukee, Wisconsin. Mr.L.Lyons of the Forest Insect Laboratory, Sault Ste.Marie, Ontario, gave me specimens of Conophthorus coniperda (Sz.) and Q.. resinosae Hopk , , and the United States National Museum, Smithsonian Institution, loaned specimens of Ips calligraphus (Gem.), I. borealis Sw., Pithophthorus consimilis Lee. and f. puberulus Lec. For valuable criticism offered in the preparation of the manuscript by Dr.E.M.DuPorte, Macdonald College, and members of the Forest Insect Laboratory, Sault Ste.Marie, Ontario, I am very grateful. Photographic reproduction of the drawings were made by Mr.D.C.Anderson and Miss E.Heino. Dr.M.L.Prebble, Chief, Division of Forest Biology, Science Service, Department of Agriculture, Ottawa, kindly granted permission for the use of the departmental data included in this thesis. II. REVIn4 OF LITERATURE There are many important and useful publications classifying the species of Coleoptera on the basis of imaginal characters. Perhaps the most noteworthy of these in North America are Blatchley's (1910) Coleoptera of Indiana and Blatchley and Leng (1916) Rhynchophora or Weevils of North Eastern America. Also, classifications to families of coleopterous larvae have been published by a number of authors with - 4 - five very useful ones appearing in the English language. MacGillivray (1903) published a key to some of the more common families of coleopterous larvae, although determinations to many larvae were incorrect according to Peterson (1951). A more comprehensive and accurate key to most families of Coleoptera was published by Roberts (1930). Boving and Craighead's (1931) illustrated key to the principal larval forms of the order is an excellent article on this subject, particularly for advanced students. Keys to the families of larvae of beetles of the British fauna were published by VanEmden (1942). Finally, Peterson (1951) published the results of his study of larval Coleoptera, his revision of Robert's key resulting in a form more satisfactory than the original for North American species. While the keys are to families only, the book is profusely illustrated with diagrams of many species of each family featuring their diagnostic characteristics. Classifications of species of Scolytidae have been based almost solely on imaginal characters, a number of the most important taxonomic papers being those of Swaine (1918), Blatchley and Leng (1916), Hopkins (1909 and 19l5a and 1915b), Chamberlin (1939), Dodge (1938) and Beal and Massey (1945). To my knowledge, only one author has attempted a comprehensive classification of bark beetle larvae, Hopkins (1909), who included in his treatise on the genus Dendroctonus a division of the species of that genus based on larval characteristics. Earlier, in 1905, the same author stated that larval characters referred the species of Dendroctonus into practically the same position as had the adult characters and my even have indicated